Internal combustion engines, including diesel engines, gasoline engines, gaseous-fuel powered engines, and other engines known in the art generate a complex mixture of exhaust gases and particulates. Components of the exhaust gases may include, among other things, oxides of nitrogen (NOx). Exhaust emission standards have become more stringent, and the amount of NOx emitted to the atmosphere by an engine may be regulated depending on the type, size and/or class of engine.
In order to comply with the regulation of NOx, some engine manufacturers have implemented a strategy called selective catalytic reduction (SCR). SCR is an exhaust aftertreatment process where a reductant, most commonly urea ((NH2)2CO) or a water and urea solution, is selectively injected into the exhaust gas stream of an engine and adsorbed onto a downstream substrate. The injected urea solution decomposes into ammonia (NH3), which reacts with NOx in the exhaust gas to form water (H2O) and diatomic nitrogen (N2).
Temperatures associated with SCR implementation may approach or exceed 200° C. In particular, high temperature exhaust gases and heat generated by exothermic reactions within aftertreatment components may heat the packaging of the SCR system. Removal of heat from the SCR system is especially problematic in stationary applications where airflow over the system may not be sufficient to readily cool the system. This high temperature environment presents particular problems for locating sensors and associated electronics required for ensuring emissions compliance.
U.S. Pat. No. 7,192,463 discloses an arrangement for disposing sensor electronics on a diesel particulate filter.